did you unwrap your UVs?It seems that you're using default 'run-time' or 'self-generated' flat UV mapping in blender (no layer to which the UV applies, it should show 'UV' in the panel). You must explicitely set the UV mapping for proper export to Octane.

In your texture panel, the field named 'Layer' should show the UV map, ie the relationship between your mesh surface and a flat image. This doesn't come up automatically and without setting it up, even if Blender may does the right guess, you can't rely on it and must provide a proper one (from blender itself).